Question 831090
Let {{{ t }}} = brother's time in minutes to paint it alone
Add their rates of painting to get their
rate working together
( 1 house ) / ( 24 min ) + ( 1 house ) / ( t min ) = ( 1 house ) / ( 15 min )
{{{ 1/24 + 1/t = 1/15 }}}
Multiply both sides by {{{ 24*15t }}}
{{{ 15t + 15*24 = 24t }}}
{{{ 9t = 360 }}}
{{{ t = 40 }}}
It will take his brother 40 min working alone